This invention relates to the field of electric or electronic circuits which are embedded within a dielectric and applied to a curved surface. The invention is especially useful in manufacturing circuits which are intended to operate in harsh environments.
As used herein, the term “circuit” is used in its broadest sense, to include any pattern of electrical conductors which accomplishes some useful object. Such circuits may be active or passive.
One example of the use of the present invention is in the aerospace and defense industries. It may be necessary to provide circuitry as a covering for the nose cone or radome of a missile, or the nose of an aircraft, to act as shield against radio frequency (RF) energy, or as an electromagnetic shield. Certain circuit patterns may be capable of blocking incoming radiation while remaining transparent to radiation transmitted by an internal antenna within the missile or aircraft. The invention is not necessarily limited to use in the above field, but could be used in other areas.
In the applications described above, the circuit which is applied to a nose or nose cone must be extremely rugged, and must withstand extreme conditions of pressure and temperature, without degradation. The circuit must be capable of withstanding the extreme heat encountered when a missile is traveling at high velocity within the atmosphere, or when a space vehicle re-enters the atmosphere, or when an aircraft is traveling at high speeds. The circuit must not be affected by other environmental factors, such as extreme cold, water, rain, or erosion.
To achieve the desired degree of ruggedness, the circuit is preferably provided in the form of a conductive cermet, embedded between layers of a compatible dielectric material, having the same or better environmental performance as the cermet. In the examples given above, this embedded circuit could be formed on the nose cone or nose, or other structure.
A “cermet” is a material containing particles of metal dispersed in a ceramic carrier. Initially, the cermet may take the form of a paste. When fired at high temperatures, the metal particles melt and fuse together, so that the metal particles become an integral electrical conductor which remains conductive when cooled. In this specification, the terms “conductive cermet” and “conductive material” will be used to include the cermet paste, although it should be understood that the material does not actually become electrically conductive until it has been fired. Examples of such cermet materials, and of their uses, are given in U.S. Pat. Nos. 4,897,676 and 6,553,662, the disclosures of which are incorporated by reference herein.
In the specific applications described above, it is important that the circuit be applied with precision, so that it has uniform geometry and significant thickness. When using the techniques of the prior art, such precision is virtually impossible to achieve when it is desired to apply the circuit to complex curved substrate surfaces, such as an ogive nose cone.
The present invention provides a practical and economical method and apparatus for applying rugged electronic circuits, of the type described above, and to many other types of curved surfaces.